Stabilized mineral oil composition



1 Patented a. 15, 1940 v 1 'UNITED -STATES PATENT OFFICE; my 2,21s,2s3fj i .c STABILIZED INERAnon. ooMrosrrIon Everett W. Fuller, Woodbury, N.J.,-assignor to. I

.Socony-Vacuum Oil Company, Incorporated, 7 7 eNewYork,N.rY.,acorporationofNewYoi-kh V No Drawing. Application March8,1939, -SerialNo.260,'5 17 j, s V

6 Claims'. (01. 252-47) I I This invention is concemed'with thestabiliza tion of viscous mineral oil fractions'against the I harmfuleffects of oxidation or deterioration with use by means of an oxidationinhibitor, or an. 6 "antioxidant. The invention is more specificallyrelatedto the improvement orstabilization of such mineral oil'fractionsby the use of novel I compounds, or a novel class of compounds, which Vwhen admixed with a viscous mineral oil in minor proportions will,preventor'dela'y 'unde-' I sirable' changes taking placein. the oil.

As is well known to those familiar with the art, substantiallyallthev'arious fractions obtainedfrom mineral oils and refined for'theirvarious usesare susceptible to oxidation. The

susceptibility of an oil fraction to oxidation and the manner inwhichoxidation manifests itself within the oil varies with the type anddegree of refinement to whichthe oil has been subjected and with theconditions'und'er which it is used or I 1 tested.. In other words-theproducts formed in.

"an oil fraction as/a result of-oxidationand the' degree to which theyare formed depends upon the extent to which the variousunstableconstituents or constituents'which may act as oxidation.catalysts. have been removed by refining operations, and also upon theconditions o fuse. A highly refined viscous oil, I for example, which isone that has been refined by treatment I 80 with fuming'sulfuric acid orother means or combinations such as AlCla, solvents and acids (or withlarge quantities of concentrated sulfuric acid), tends to formrelatively large amounts of.

. acidic constituents whensubjected to oxidizing conditions. Thepresence'of catalytic materials such as copper does not appear to affectappreciably the oxidation of highly refined oils and such oils are lessprone to the formation of colored bodies or of insoluble sludge. Theformation of 4 acidic bodies, however, is highly undesirable=for mostapplications of these oils. For example. when used as an insulatingorcooling oil in electrical equipment such as .transformers'orcapacitors an increase in acidic bodies tends to lower'the div: 5electric strength of the oil'and has-other harmful efiects which areundesirable. The acids are cor- 'rosive to metals and thus reduce theuseful life of the oils as lubricants or for other purposes in whichthey come in-contact'with metals, and the acidic materials are alsoinjurious in textile lubri- V cants and in spray oils. 7

Moderatelyrefined oils, which are normally. 7

oils that have been refinedby treatment with only moderate amounts ofsulfuric acid, or other refining agents; tend to form relatively smallrefinedoils, but considerably less than with highly refinedoils. Bothsludge and acid formation;--

- lower theirfvalue for many purposes, such 'aSj25i amounts of acidicoxidation productsaas-com vpared with highly refined oils, but theyundergo imaterial color'depreciation and form considerable amounts ofsludge. The changes taking place in V V 7 these oilsare appreciablyaccelerated by the 6 presence of.meta1 catalysts-such as copper,'Suffi-" cient acid is'generally formed to cause some re-' ductioninthedielectric strength of these 0115';

but the. principal objection 'to the'm is their 7 I tendency to depositsludgewhich interfers with 10 p a heat transfer in transformers andturbines and also causes plugging 'of oil feed lines in lubricating V vsystemssolvent refined oils: in general which have been prepared bytreatment with selectivesol- 16,

vents, such as chlorex, phenol, furfural; etc.; resemble the moderatelyrefined acid-treated oils in i .that their oxidation is accelerated bythe presence of metals such as copper and further in that it is attendedby substantial color depreciation and 20 sludge formation. 'Acidformation is usually greater than in the case of moderatelyacidhas beensuch as to make them intermediate in properties between'the types setup- Thus, respouse to inhibitors may be said to depend em; tirely on thetype of oxidation and end products of oxidation of an oil, which in turndepends largely upon the degree of refining this oil has had.

Further, the degree of refining required to produce these types of oilsvaries with the crude source 5 so that any one refining procedure mayproduce either a highly refined oil ora moderatelyrefined oil, dependingupon the crude source. .Pennsylvania type oils,'for example;requireimuch less refining to produce highly refined oils than 50 theCoastal type of oils. r r V V J The use of oxidation inhibitors for thepurpose 5 of stabilizing a viscous-mineral oil fraction against a thedeleterious efiects of oxidation'discussed above is'wellk'nown 'Sincetheaction ofthe'seinhibiting i (Ber. 24, 1403).

2 materials is apparently catalytic the problem of their development isa difiicult one and is evident- 1y influenced to a large degree by theoxidizable constituents which are in the oil following a particularrefining treatment. Thus a particular inhibitor or class of inhibitorsmay be effective to stabilize a highly' refined oil against acidformation while the same inhibitor may have no appreciable effect uponacid, color or sludge formation in a moderately refined oil and viceverse. This same inhibitor may or may not be effective in inhibitingacid, sludge and color formation in a solvent-refined oil and mayor maynot be effective to inhibit the corrosive action of a solvent-refinedoil toward metals such as used in cadmium-silver bearings.

This invention is particularly concerned with the inhibition ofoxidation of the type used in transformers, turbines, and the likethrough the use of a novel class of compounds to be hereinafterdescribed. The compounds contemplated herein do not appear to beeifective negative catalysts toward the oxidation of moderately refinedor solvent-refined oils of the turbine oil type, but I have found thatcertain of the compounds belonging to the general class contemplatedherein are efiective to inhibit corrosive action of solvent-refinedmotor oils toward alloy metals, such as cadmium-silver alloy bearings,under conditions encountered in crankcase use.

My invention is predicated upon the discovery that a class of organiccompounds which may be broadly termed mercapto benzo thiazoles and theirderivatives are effective negative catalysts toward the oxidation ofviscous mineral oils of the highly refined type.

The mercapto benzo tives thereof contemplated as oxidation inhibitorsfor the mineral oil blends contemplated herein may be represented by thegeneral formula:

wherein R. represents hydrogen, an alkyl group or an aryl gro p, andX-represents hydrogen or the radical Compounds of the general typecharacterized by Formula A in which X represents hydrogen are themercapto benzo thiazoles, such a compound in which R also representshydrogen being l-mercapto benzo thiazole. Compounds of the typecharacterized by Formula A where X represents the radical A are benzothiazyl disulfldes, such last-mentionedv compounds being oxidationproducts of the corresponding mercapto benzo thiazoles.

The mercapto benzo thiazoles can be prepared by heating an azobenzenewith carbon disulfide On treating a solution of a in highly refined oilstar test, involved heating a thiazoles and the derivaindicated bygeneral mercapto benzo thiazole with an oxidizing agent, such aspotassium dichromate, the corresponding benzo thiazyl disulfide isobtained (same reference). Other methods for preparing these compoundsare given in the literature.

The following examples illustrate the effectiveness of the class ofcompounds contemplated herein as oxidation inhibitors for viscousmineral oils by certain specific compounds within the class.

Exmms I Highly refined oil The oil employed in this test was of thehighly refined type used in transformers and the like which had beenobtained from a Coastal distillate by successive treatments with 40 lbs.per bbl. of 98 per cent sulfuric acid and 180 lbs. per bbl. of 103 percent oleum, followed by neutralization, washing and clay percolation. Ithas a specific gravity of 0.871, a flash point of 310 F. and a Sayboltviscosity of 69 seconds at 100 F.

The test used, known as the Modified German 150 gram sample of the oilat a temperature of 120 C. while bubbling oxygen gas through the oil fora period of '10 hours. The quantity of acidic'oxidatlon products formedwas determined by: (a) extracting the oil with alcoholic soda,neutralizing the extract, and then weighing the precipitated material,which is calculated as per cent acidic tar; and (b) by titrating theacids formed in the oil with alcoholic KOH and expressing the result asthe neutralization number (N. N.) which represents the milligrams of KOHrequired to neutralize the acid in one gram of oil.

The results of this test, using representative compounds of the typecontemplated by this invention, are listed in Tables I and 11 below. InTable I the compounds used are of the type Formula A above, where R ishydrogen. In Table II the compounds are of the type represented bygeneral Formula A, wherein at least one R represents an alkyl group oran aryl group and the remaining Rs represent hydrogen.

Table I Acidic Oil tar Percent 01] alarm 15 Oil-+03% mercapto benzothiazole 0. 02 Oil saturated (0.02- l-%) with benzo thiazyldixulflde-----. 0. (I!

a Table II Oil N. N.

Oil alone... 25. Oil+ .10 methyl mercapto benzo thiazole 0. 01 Oili mphenyl mercapto benzo thiazole. 0. 02 Oil .l0 diEniethyl benzo thiazyl)disulflde... 0. 01 Oil+ .l0% dl phenyl benzo thiazyl) disulflde-.- 0. 01

From the foregoing results it will be seen that both the unsubstitutedand the substituted mercapto benzo thiazoles and their correspondingoxidation products, the benzo thiazyl disulfides, are effectiveinhibitors of acid formation in oils of the highly refined type:

VEXAMPLI II Solvent-refined motor oil The substituted mercapto benzothiazoles and their corresponding disulfldes were also found to be ofmeasurable effectiveness in inhibiting the corrosive action ofsolvent-refined motor ofl toward alloy metals of the type used incadmiumsiiver bearings. The oil used in this test was one obtained byseparately refining Pennsylvania neutral and residuum stocks withchlorex and blending to give an oil of the following properties:

specific gravity 0.872; flash point 435 F., and,

Saybolt viscosity of 318 seconds at 100 F.

The test used involved immersing a fi-gram section of a cadmium-silverbearing of the type used in connecting rods in. a. 30-gram sample of theoil, heating the oil to a temperature of 175 C.

and bubbling air therethrough against the surface of the bearing for aperiod of 22 hours. Two

specimens from the samebearing were tested simultaneously, one in theoil alone and the other in "oil containing the inhibitor. I

In Table III below the losses in weight of the respective metalspecimens in the oil alone and the oil containing the inhibitor arelisted in the 7 columns headed Not. inh." and Inh., respectively, suchlosses being a measure of corrosiveness of the oil or oil blend towardthe alloy of f the test specimen.

Table III Loss in weight (mgs.) Inhibitor Amount Not. inh. Inh.

I Methyl mercapto benzo thiazole... 25% 78 28 Phenyl mercapto benzothiazole 25% 78 40 Di(methyl benzo thiazyl) disulfide. 25% 73 12Di(phenyl benzo thiazyl) disulfide 25% 73 52 It will be understood thata suitable, solvent such as benzene may be employed if desired tofacilitate solution of the improving agent in the oil; also that thecompounds contemplated herein may be used in varying amounts, dependingupon the oil fraction, conditions of use, etc., but for the purposescontemplated herein it has been found that the use of these compounds inamounts 7 ranging from about 0.01 per cent to about 0.5 per cent willgive satisfactory results.

It is to be further understood that the terms highly refined andsolvent-refined as used herein have reference to oils correspondingsubstantially in their manner of deterioration and 7 inhibitor responseto the examples given and are prising a highly refined viscous oil ofthe type 15,

used in turbines,.transformers, and the like having in admixturetherewith a minor proportion, suflicient to substantially inhibit thedeleterious 'eifects of oxidation on said oil, of a. mercapto benzothiazole. I 2. An improved mineral oil composition comprising asolvent-refined viscous mineral oil fraction having in admixturetherewith a minor proportion, sufi'icient to substantially inhibit thedeleterious effects of oxidation on said oil, of a mercapto benzothiazolein which the arylnucleus has at least one substituent selectedfrom the group consisting of alkyl and aryl hydrocarbon groups.

3. A viscous mineral oil fraction containing from about'0.01 per cent toabout 0.5 per cent of a mercapto benzo thiazole. V

4. A highly refined viscous mineralfoil fraction normally tending todevelop acidic. products under oxidizing conditions and in admixturetherewith a minor proportion of l-mercapto benzo thiazole, suflicient tosubstantially inhibit the development of said acidic oxidation products.

5. A highly refined viscous mineral oil fraction normallytending todevelopacidic products under oxidizing conditions and in admixturetherewith a minor proportion of methyl mercapto benzo thiazole,sufficient to substantially inhibit the .development of said acidicoxidation products;

6. A highly refined viscous mineral oil fraction 'normally tending todevelop acidicproducts under oxidizing conditions and in admixturetherewith a minor proportion of phenyl mercapto benzo thiazole,sufiicient to substantially inhibit the development of said acidicoxidation products. EVERETT W. FUILER.

